This application claims priority under 35 U.S.C. 119 from Singapore Application No. 200105517-7 filed Sep. 10, 2001, which application is incorporated herein by reference.
The present invention relates generally to integrated circuit manufacturing equipment, and in particular to apparatus and methods for dicing wafers.
Wafers are fabricated with a plurality of dies each having a plurality of integrated circuit elements therein. A die represents one individual chip that must be separated from adjacent dies before packaging. Conventionally, dies are separated from each other and the rest of the wafer by a saw blade. With the existing dicing technology of using diamond-nickel blades, the backside cutting quality can be improved by performing a two-pass cut. However, this will reduce productivity by around 50% and a wider saw kerf is expected. This is due to machine accuracy for the second pass. The wider saw kerf hinders progress towards a smaller saw street and thus leading to a lower die per wafer count.
Another area of concern when separating the dies is chipping on the top surface of the dies or fragmentation on the bottom surface of the dies adjacent the saw street. It is believed that one the of possible causes for the top or bottom surface fragmentation detected after the dicing process is the presence of a passivation layer, test structures, and/or metal layers deposited on the saw street during various wafer fabrication processes. These materials are not removed during wafer fabrication due to the higher operational cost and cycle time required for such fabrication steps. The impact of these materials on the cutting quality can be seen in FIG. 1. The reason for this poor cutting quality is believed to be due to the clogging of the blade, which results in overloading of the blade during dicing.
It is believed that a two-pass cut process using a saw blade for each cut pass will not significantly improve topside chipping as compared to a single-pass cutting due to the presence of test structures and metal layers on the wafer. The cutting quality of a two-pass cut can be seen in FIG. 2. A comparison on the cutting quality obtained from a single-pass cut and a two-pass cut is shown in Table 1.
The numbers associated with the back side chipping and back side cracking represent the size, e.g., length or width, of such defects in microns. As shown in Table 1, the backside chipping and cracking improves approximately 40-50% using a two-pass cutting process. The top side chipping, for example, in its width, does not improve significantly in a two-pass cutting process.
While saw cutting of wafers is the conventional industry standard, there remains drawbacks with such cutting. Saw blades wear over time. This results in inconsistent cutting quality from when the blade is new and subsequent cutting operations. Consequently, the operator must predict when the blade has reached the end of its useful life. This can not be predicted accurately. Accordingly, the saw blades may be changed before the end of their useful lives resulting in higher equipment costs than necessary due to premature saw blade replacement. Moreover, saw blades introduce mechanical stresses in the workpiece while sawing, especially at the surfaces of the workpiece. Due to these stresses saw blades may not be used to cut very thin workpieces, such as ultrathin semiconductor wafers.
A recent development in wafer dicing is laser cutting. However, laser dicing of semiconductor wafers have failed to meet the rigid demands of industry. One significant drawback of using lasers is the collateral thermal damage to the chips caused by the laser. New lasers have been proposed to overcome the drawbacks of conventional lasers in the area of semiconductor dicing. An example of such a system is being promoted by Synova SA. of Lausanne, Switzerland, and described in WO 99/56907, titled xe2x80x9cMATERIAL SHAPING DEVICE WITH A LASER BEAM WHICH IS INJECTED INTO A STREAM OF LIQUIDxe2x80x9d, herein incorporated by reference. WO 99/56907 describes a method and device for shaping material of workpieces using a laser beam which is injected into a stream of liquid. The liquid, which is to be formed into a stream, is fed to the nozzle channel opening such that the liquid does not swirl, especially without flow components which are tangential to the nozzle channel axis. The laser irradiation is focused on a channel entry plane and the liquid is fed to the channel opening in such a way that a liquid retention space is avoided in a beam focusing ball and in the immediate surroundings thereof. Another laser cutting arrangement is described in U.S. Pat. No. 5,902,499, herein incorporated by reference. However, these laser cutting arrangements require a reduced speed when used to cut wafers. The feedspeed of the wafer is reduced to 40 mm/s and 20 mm/s for wafers with 305 xcexcm and 470 xcexcm thickness, respectively. This is due to the greater laser pulse energy required. Therefore, with this method, laser cuts can be achieved at the expense of productivity.
For the reasons stated above, for other reasons stated below, and for other reasons which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for improved integrated circuit manufacturing equipment and methods of manufacturing integrated circuits.
The present invention is directed to methods and devices for cutting workpieces, which include a laser adapted to at least partially cut a workpiece. In an embodiment, the workpiece is a wafer having a plurality dies each with an integrated circuit. An embodiment of the present invention further includes a mechanical cutter following the laser and engaging the workpiece. An embodiment of the mechanical cutter includes a cutting blade adapted to complete a cut through a workpiece. An embodiment of the cutting blade includes a nickle-diamond cutting surface on a circular blade. An embodiment of the laser includes a liquid guided laser beam. An embodiment of the laser includes a yttrium-aluminum-garnet (YAG) laser.
In an embodiment, a process according to the present invention includes a two-pass cutting procedure. The first pass is made by a laser, which scribes the workpiece. The second pass is made by a mechanical cutter. In an embodiment, the mechanical cutter follows the scribe created by the laser. In an embodiment, the workpiece is supported by a table. The workpiece moves relative to the laser and the mechanical cutter. In an embodiment, the relative movement of workpiece is at a speed of about 120 mm/sec.
These and other embodiments, aspects, advantages, and features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims.